1. Field of the Invention
The invention relates to a method for applying a decorative-layer made of an electron beam-curable coating mass, in particular a lacquer, a glue, an adhesive or a mixture of some or all thereof, on a backing plate and/or on a web-formed substrate, wherein the decorative-layer is sufficiently treated with high-energy radiation, particularly UV-radiation, x-ray-radiation, laser-radiation and/or electron radiation, at a certain temperature and normal pressure, such that it will be crosslinked and/or polymerized until the decorative-layer has reached a desired hardness.
2. The Prior Art
EP 0 166 153 B1 discloses a decorative plate which comprises a nuclear-coating, one- or two-sided decorative layers, as well as a limit layer, on at least one of the two plate surfaces. The limit layer is mainly made of a synthetic-resin, out of one or more, through radiation polymerized components, which are chosen from the group of unsaturated acrylates and methacrylates. This limit-layer, through radiation polymerized, is pressed under a pressure of 10 bar and at a minimum temperature of 80xc2x0 C., so that this limit layer has a scratch-demand of about at least 2, preferably is scratch proof from 2 to 7 newton.
The components used have a strong inclination to polymerize radically during the influence of actinious radiation. As actinious radiation, near UV-light or high-energy radiation, e.g., electron-corpuscular-radiation or x-ray radiation, can be a possibility. When curing under the effect of actinious radiation, photoinitiators will be added which absorb the UV-light and which can facilitate, under the formation of radicals, the introduction of the radical polymerization. On the other hand, when curing with electron beam, photoinitiators are not necessary.
The electron beams which are used for the curing of the polymerizable compounds suitably have a corresponding energy of about 150 to 350 keV.
Actually, the application of coating masses occurs by rolling, casting or spraying on the plate-formed substrate. For web-formed materials among other things, multiple-roller-feeder, air jets, air knifes and the like are used.
The curing of the applied coating masses through high-energy radiation occurs under an inert gas atmosphere. The chemical affinity to oxygen of radicals formed by the influence of high-energy beams is higher than the affinity of the radicals among themselves. The consequence of this is that chain-breaking-reactions take place at the contact-surfaces between coating masses and air, which lead to useless surface-qualities on account of the defective molecule sizes.
In order to avoid these disadvantageous consequences, an inertization with nitrogen, carbon dioxide, exhaust of a stoichiometric combustion or a noble gas is employed. This inertization causes comparatively high running costs and consequently a very high technical effort on the part of the line-construction. In order to produce an acceptable surface-quality, this expensive construction in the past could not be avoided. Other systems, for example vacuum-inertization or curing under a thin water layer, turned out to be more expensive and less practicable. The matting, or rather the matting rank of the surface of the carrier foil, is reached by the input of additives. With it, the below limit of solvent free systems stays at a gloss rank of 45 at 60xc2x0 according to Lange. A big share of matting-agents reduces the surface quality and leads to problems during the processing.
The development of a structured surface can only occur in narrow limits and partially in undesired forms, by applying the several application-systems, e.g., roll-structure with visible application direction. A change of the structure during the production-process is very costly and therefore commercially not realizable.
For the irradiation of a coating mass with high-energy radiation, a radiation chamber will be filled up with inert gas in a way that a residual oxygen content will be tuned, which normally lies between 10 to 1000 ppm oxygen. From this result surfaces which are sufficient for the actual demands.
The treatment in casing-, rolling- or spraying-machines requires a certain viscosity regarding the coating masses. This viscosity is reached by the addition of so-called xe2x80x9creactivity thinner.xe2x80x9d These mostly are low-molecular, one- or multiple unsaturated compounds, mainly acrylic-acid-residues, e.g., hexandiol-1.6-diacrylate. First of all, these monomers, as a result of their minor molecular weight and their marked chemical activity, are responsible for the negative trade-hygienical features of beam curable lacquers. These appear by inexpert treatment in form of skin- and mucous-membrane-irritation.
Today it is calculated that only 5% of the used lacquer quantity still remains on the plate as a solid after the application of the coating mass through spraying. With casting or rolling, a good exploitation of the inserted lacquer quantity will be reached, but a coating of profiled surfaces in fact isn""t possible.
The prevailing used possibility, to give a structure to plate-formed materials, is the structuring of dividing-sheets, rolls or double-bands, which are utilized for the plate-production. This system is costly and moreover has the disadvantage that a small damage of the sensitive dividing-sheets, rolls or double-bands leads to the effect that the dividing-sheets, the rolls or the double-bands become useless and they have to be replaced by new dividing sheets, rolls or double bands.
In conventional coating-masses, for example in NC-lacquers, incident dust sinks and after the curing it isn""t visible. By solvent-free systems the dust remains on the uncured coating mass and after the curing it is disturbing visible. With costly designed pure-chamber-lines with intake air super filtration, it was tried to shield the wet coating from the dust incidention. Mostly the results aren""t satisfactory, this regards mainly the spray-application.
The necessary viscosity for the processing on conventional coatings can be adjusted by the addition of solvents. In beam curable systems, so-called xe2x80x9creactivity thinnersxe2x80x9d are used.
The object of this invention is to develop a method for the application of a decorative layer on a carrier-plate such that a decorative-plate can be cured without inert gas, whereby the substrate has a high scratch-resistance, a very good weather-resistance and wherein the plate can achieve any gloss-rank and any structure.
For achieving this object it is intended:
that in order to protect the decorative-layer, which has to be cured, against the influence of oxygen, on one side it will be covered by the substrate forming the carrier-plate, and on the other side it will be covered by a foil, for example, by a carrier-foil,
that the irradiation of the decorative layer with high-energy radiation will be conducted in an inert gas-free atmosphere, and
that a pressure adequate to the level of the atmospheric pressure will be tuned and during the influence time of the high-energy radiation it will be maintained.
In this way a system for the application and the structuring of a decorative layer on a carrier plate is obtained which doesn""t have the above-mentioned disadvantages and which to the contrary is developed in a way that the plate with the applied coating mass can be cured without inert gas and which is characterized by a special high scratch-resistance and a very good weather-resistance. It is possible to give to the plate any gloss-rank and any structure.
In this system there exists no contact-surface between the coating mass and air, so that no radical chain-breaking reaction due to the effect of oxygen takes place. The coating mass, which has to be cured, and the out of this formed decorative layer on the one side will be covered by the substrate and on the other side it will be covered by the carrier foil and so it will be protected against the influence of oxygen.